Surfactants are a group of organic compounds that are of increasing concern. They are a group of chemicals that are in widespread use around the world with global production exceeding 9.86×109 kg per year. Surfactants are used in large amounts daily in households around the world in cleaning products and detergents, in industrial applications including the manufacturing of pesticides, plasticizers in the cement and concrete industries, mining, pharmaceuticals and many other products.
Anionic surfactants are the major class of surfactants that are used in detergents. Linear alkylbenzene sulfonate (LAS) is published to be the most widely used anionic surfactant. Wastewater treatment facilities receive anionic surfactants in significant amounts due to the enormous use of detergents for washing purposes and from other sources. While most of the surfactants are able to be eliminated through conventional wastewater treatment, some surfactants have low biodegradability and, in others, undesired biodegradation products are formed and discharged with effluents into surface waters. Another route for introducing these chemicals into the environment includes the use of sewage sludge as fertilizer in agriculture. The surfactants can leach into the surrounding soils and be further transported to groundwater and surface waters.
One particular class of specialty surfactants, fluorinated surfactants, have properties that make them particularly well suited to fire-fighting applications. PFOS (perfluorooctane sulfonate C8F17SO3) and PFOA (perfluorooctanoic acid C7F15CO2H) are two commonly used fluorinated surfactants. These surfactants have been detected in human blood, water, soils, sediments, air, and biota samples. The compounds have been found to be globally distributed, persistent and bioaccumulative.
In order to be able to detect anionic surfactant contamination in the environment, various assays for the detection of anionic surfactants have been developed.
The Methylene Blue Active Substances (MBAS) assay is the current standard colorimetric test used to estimate the concentration of anionic surfactants in water. The water sample is acidified, 3 mL of chloroform and a methylene blue solution is added, then the sample is agitated. In the MBAS assay, the anionic surfactant complexes with the cationic dye. The higher the concentration of anionic surfactant, the more the dye is absorbed and the greater the colorimetric change. For method sensitivity, LAS is used to estimate the concentration of anionic surfactant, and concentrations are reported in LAS equivalents. The MBAS assay has a published detection limit of 0.025 mg/L.
While this method has been used extensively, the use of the assay is problematic since it uses chloroform as the extraction solvent, which is a suspected human carcinogen. Thus, a need exists for an improved assay for the detection of anionic surfactants. It would be desirable that such an assay would eliminate the use of the suspected carcinogenic solvent, chloroform. It would also be desirable if an improved assay was suitable for use in the field for the rapid detection of anionic surfactants in environmental samples.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.